Enable quiet mode when writing output to stdout
Created by: Ede123
If quiet mode is not enabled when writing SVG output to stdout, all informational text output ends up mixed into the SVG output (notably the status report at the end, e.g. "Scour processed file "x.svg" in 21 ms: 5708/13196 bytes new/orig -> 43.3%")
This fixes #47 (closed).